With rise of modern energy, iron & steel, electric power, military and aerospace industries as well as development of such industries as petroleum, natural gas and modern chemical engineering, valve and valve actuator become indispensable and important product in industry control, and in the fluid control field and valve automation industry, valve actuator is a necessary valve driving device for realizing remote control and self-control of the valve. As control process and control requirement increase, electric valve actuator fails to meet requirement any longer on such aspects of electric explosion protection, speed of action and response time, therefore pneumatic-hydraulic actuator, electric-hydraulic actuator and the like emerge at this right moment. And shift fork transmission mechanism is the most important component of the actuator.
In pneumatic, hydraulic, pneumatic-hydraulic and electric-hydraulic actuators of shift fork transmission mechanism, shift fork transmission box (shift fork box) composed of a shift fork box body and a shift fork transmission component acts as an important part, and the shift fork box is also an important part of the shift fork type valve actuator. The shift fork type actuator is a shift fork transmission mechanism composed of a shift fork box, a guide shaft, a shift fork and a shift fork component; under thrust of air cylinder (hydraulic), linear motion of air cylinder piston is converted into a transmission structure that shift fork shaft outputs in a form of motion at a pendulum angle through a transmission sliding block. The shift fork type actuator is subject to a working characteristic that output torque of the actuator is changed as rotating angle of the shift fork becomes different in a transmission process, wherein output torques on left and right sides are the maximum ones and the output torque on the middle position is the minimum one. This characteristic is consistent with a rule that torque value on the position that a rotary motion valve is opened or closed is the maximum and the torque on the middle running position is the minimum, thus avoiding torque waste and minimizing required cylinder diameter; and shift fork of the shift fork pneumatic actuator is highly overlapped with shift fork arm; so that space is greatly saved.
Pneumatic actuator includes pinion-and-rack pneumatic actuator and shift fork pneumatic actuator: the pinion-and-rack pneumatic actuator, on the basis of pinion-and-rack engagement driving principle, must guarantee long and thick gear of gears of wheel disc, and two gears, when keeping 0 degree, can be engaged constantly without separation while can be completely engaged when keeping a right angle; therefore, heavy size of this pinion-and-rack pneumatic actuator is determined fundamentally, and the expression of being heavy is more obvious as the torque is higher; thus, shift fork pneumatic actuator emerges; the shift fork pneumatic actuator not only meets an explosion-proof requirement, but also is small in size, light in weight and large in torque; the shift fork actuator, which adopts unique transmission structure design of “single cylinder and dual pistons-shift fork variable torque”, is produced in accordance with high requirement on working condition; the shift fork pneumatic actuator will dominate the industry in the future.
The present shift fork transmission mechanism, which has no or any one guide shaft, just keeps one force arm distance between oil cylinder (oil cylinder) piston output shaft on the side of the shift fork box and shift fork transmission shaft, therefore lateral force is subsequently generated, which not only reduces transmission efficiency and increases lateral stress on shift fork bearing, air cylinder piston and bearing, but also reduces output rigidity of piston shaft; and the shift fork may be instable in running, thus causing influence on reliability of transmission.